to_string.cc

#include <cstdlib>

#include <string>

// All of the below are not really standards-compliant, but good enough
// for experiments.
void* operator new(std::size_t size) {
  printf("Calling new(%zu).\n", size);
  return std::malloc(size);
}

void operator delete(void* pointer) noexcept {
  std::free(pointer);
}

void* operator new[](std::size_t size) {
  printf("Calling new[](%zu).\n", size);
  return std::malloc(size);
}

void operator delete[](void* pointer) noexcept {
  std::free(pointer);
}

/**
 * This is a demo of the small string optimization - the effect of which here is that
 * std::to_string will almost never allocate heap memory. In particular, it never does on
 * the tested version of clang, and only allocates memory for numbers with more than 15
 * digits on G++ 5.0.
 *
 * For details, look at this article: http://blogs.msmvps.com/gdicanio/2016/11/17/the-small-string-optimization/
 * or many of the others available online.
 */
int main() {
  // Comments are about the behaviour with clang-800.0.42.1.
  // Yes, this is a memory leak.
  auto s = new std::string; // prints "Calling new(24)."
  std::string s1; // doesn't print anything.
  auto num = std::to_string(1234); // doesn't print anything.
  printf("%zu\n", num.length()); // prints "4" and nothing else.
  printf("%zu\n", std::to_string(123456789123456789LL).length()); // prints "18" and nothing else.
}